Bug 797532 - Crash/Coredump Lots

Replace the asserts in cap-gains.c with g_return_val_if_fail. There's
nothing about cap-gains.c that justifies crashing the program.

libgnucash/engine/cap-gains.c

@@ -336,7 +336,7 @@ xaccSplitAssignToLot (Split *split, GNCLot *lot)
         amt_tot = split->amount;
         amt_a = gnc_numeric_neg (baln);
         amt_b = gnc_numeric_sub_fixed (amt_tot, amt_a);
-        g_assert (gnc_numeric_check(amt_b) == GNC_ERROR_OK);
+        g_return_val_if_fail(gnc_numeric_check(amt_b) == GNC_ERROR_OK, NULL);
 
         PINFO ("++++++++++++++ splitting split=%p into amt = %s + %s",
                split,
@@ -366,7 +366,7 @@ xaccSplitAssignToLot (Split *split, GNCLot *lot)
                  gnc_num_dbg_to_string(amt_tot));
         }
 
-        if (gnc_numeric_zero_p(val_a) || gnc_numeric_zero_p(val_b))
+        if (gnc_numeric_zero_p(amt_a) || gnc_numeric_zero_p(amt_b))
         {
             PERR ("Failed to split into two!");
         }
@@ -376,8 +376,8 @@ xaccSplitAssignToLot (Split *split, GNCLot *lot)
                gnc_num_dbg_to_string(val_a),
                gnc_num_dbg_to_string(val_b) );
 
-        g_assert (!gnc_numeric_zero_p (amt_a));
-        g_assert (!gnc_numeric_zero_p (val_a));
+        g_return_val_if_fail (!gnc_numeric_zero_p (amt_a), NULL);
+        g_return_val_if_fail (!gnc_numeric_check (val_a), NULL);
         xaccSplitSetAmount (split, amt_a);
         xaccSplitSetValue (split, val_a);
 
@@ -438,8 +438,8 @@ xaccSplitAssign (Split *split)
      * have lots, we are done.
      */
     if (split->lot) return FALSE;
-    g_assert (split->gains == GAINS_STATUS_UNKNOWN ||
-	      (split->gains & GAINS_STATUS_GAINS) == FALSE);
+    g_return_val_if_fail (split->gains == GAINS_STATUS_UNKNOWN ||
+                          (split->gains & GAINS_STATUS_GAINS) == FALSE, FALSE);
     acc = split->acc;
     if (!xaccAccountHasTrades (acc))
         return FALSE;